The field of the disclosure relates generally to a system and method for maintaining machines and, more particularly, to pilot apparatus for positioning service apparatus within machines.
At least some known machines, such as turbines for aircraft engines and gas and steam powered turbines for industrial applications, include an outer case and at least one rotor that carries multiple stages of rotating airfoils, i.e., blades, which rotate with respect to the outer case. In addition, the outer case carries multiple stages of stationary airfoils, i.e., guide vanes. The blades and guide vanes are arranged in alternating stages. In at least some known machines, shrouds are disposed on the radially inner surfaces of a stator to form a ring seal around tips of the blades. Together, the blades, guide vanes, and shrouds define a primary flowpath inside the compressor and turbine sections of the machine. This flowpath, combined with a flowpath through the combustor, defines a primary cavity within the machine.
During operation, the components of the machines experience degradation. Accordingly, for at least some known machines, periodic inspections, such as borescope inspections, are performed to assess the condition of the machines in-between service intervals. Examples of conditions observed during inspections include wear (e.g., from incursion of blade tips into the shrouds, particle-induced erosion, water droplet induced erosion, wear due to sliding contact between stationary components), impact (e.g., spallation of thermal barrier coating (TBC) or environmental barrier coating (EBC) from turbine-section components, leading edge burring/bending of compressor blades), cracking (e.g., thermal fatigue, low-cycle fatigue, high-cycle fatigue, creep rupture), edge-of-contact damage between stationary parts, oxidation or hot corrosion of high-temperature metallic sections, static seal degradation, and creep deformation (e.g., of guide vane sidewalls/airfoils, blade platforms, and blade tip shrouds).
During service intervals, the machines are at least partially disassembled to allow repair and/or replacement of damaged components. For example, damaged components of at least some known machines are primarily repaired at overhaul or component repair facilities, with only limited intervention conducted in the field. Processes used to repair compressor and turbine flowpath components include surface cleaning to remove accumulated dirt and oxidation products, stripping and restoration of coated surfaces, crack repair, section replacement, and aero contouring and smoothing. Repairing the components during planned service intervals reduces the cost to maintain the machines because the cost to repair components is sometimes less than the cost to replace the components. However, sometimes, the components run past their repair limits between planned service intervals. In addition, sometimes, heavily distressed components fail and cause an unplanned outage.
For at least some known machines, a tethered device, such as a borescope, is inserted through an opening of the machine and manipulated within a cavity of the machine for inspection. However, at least some known tethered devices do not access all locations of the machine. In particular, some non-rotating components in at least some known rotary machines are difficult to access with a tethered device. In addition, the angle of regard and distance between the inspection tool and the area of interest, combined with limited borescope orifice dimensions, sometimes precludes performance of maintenance operations even if trained borescope operators can gain visual access to areas of interest within the machine. As a result, damage detected during inspection is typically unmitigated until the machine is at least partially disassembled for service.